Introductory Remarks. 5 



of insectivorous mammals in which all the genera but one are 

 restricted to Madagascar, the one exception (Solenodori) living in 

 Cul >a and Haiti. Examples of this sort are known as cases of dis- 

 continuous distribution, and indicate that the ancestors of the 

 animals in question formerly inhabited a vast extent of country ; 

 that some sort of land connection, however indirect, existed be- 

 tween the colonies now so widely separated, and that the surviv- 

 ing descendants of these groups are probably approaching ex- 

 tinction. 



The examples thus far cited relate to the disconnected land 

 areas in the neighborhood of the equator or in the southern hem- 

 isphere, and their explanation is to be sought in the history of 

 the past. In the northern hemisphere animals and plants in 

 general have a much more extended distribution than in the 

 southern, the majority of the larger groups being common to 

 North America, Europe, and Asia, and the limits of their distri- 

 bution are encountered in traveling in a north and south direc- 

 tion and are evidently the result of causes now in operation. It 

 is to this class of cases as presented on the North American con- 

 tinent that your attention is invited this evening. 



In passing from the tropics to the Arctic pole on the eastern 

 side of America a number of distinct zones are crossed, the most 

 conspicuous features of which are well known. In the plant 

 world the palms, mangroves, mahogany, mastic, Jamaica dog- 

 wood, and cassias of the tropical coast districts are succeeded by 

 the magnolias, pawpaws, sweet-gums, hackberries, and persim- 

 mons of the Southern States. These give place gradually to the 

 oaks, chestnuts, and hickories of the Middle States, and the latter 

 to the groves of aspen, maple, and beech which reach the south- 

 ern edge of the great coniferous forest of the north a forest of 

 spruces and firs that stretches completely across the continent 

 from Labrador to Alaska. Beyond this forest is a treeless ex- 

 panse whose distant shores are bathed in the icy waters of the 

 Arctic Ocean. 



Concurrently with these changes in vegetation from the south 

 northward occur equally marked differences in the mammals, 

 birds, reptiles, and insects. Among mammals the tapirs, mon- 

 keys, armadillos, nasuas, peccaries, and opossums of Central 

 America and Mexico are replaced to the northward by wood- 

 rats, marmots, chipmunks, foxes, rabbits, short-tailed field-mice 

 of several genera, shrews, wild-cats, lynxes, short-tailed porcu- 



